Catalytic reforming of naphtha feedstocks is well known in the petroleum refining industry. Most naphtha feeds contain large quantities of naphthenes and paraffins and consequently they have low octane numbers. In catalytic reforming, these components go through a variety of hydrocarbon conversions resulting in a gasoline product of improved octane number. Some of the more important conversion reactions include dehydrogenation of naphthenes to aromatics and dehydrocyclization of normal paraffins to aromatics. Less desirable reactions which commonly occur include hydrocracking of paraffins and naphthenes to produce gaseous hydrocarbons such as methane and ethane. Due to these less desirable reactions, an important objective of catalytic reforming is to rearrange the structure of the hydrocarbon molecules to form higher octane products without any significant change in the carbon number distribution of the stock.
The reforming reactions are typically catalyzed by reforming catalysts comprising porous supports, such as alumina, that have dehydrogenation promoting metal components impregnated or mixed therewith. In a conventional reforming process, a series of reactors constitute the basis of the reforming unit. Each reforming reactor is generally provided with a fixed bed or beds of the catalyst which receive upflow or downflow feed. Each reactor is provided with a heater because the reactions which take place therein are endothermic. In a conventional reforming process, a naphtha feed with hydrogen or hydrogen recycle gas is passed through a preheat furnace, then through a reactor, and then in sequence through subsequent interstage heaters and reactors of the series. The product of the last reactor is separated into a liquid fraction and a vaporous effluent. The vaporous effluent, a gas rich in hydrogen, is used as hydrogen recycle gas in the reforming process.
During operation, the activity of the reforming catalyst gradually declines due to the build-up of coke, and the temperature of the process is gradually raised to compensate for the activity loss caused by the coke deposits. Eventually, economics dictate the necessity of regenerating the catalyst. Furthermore, the presence of halogens such as chlorine during regeneration results in the formation of corrosive by-products such as HCl and NH4Cl. These compounds can cause damage to equipment used in the reforming process such as heat exchangers, liquid/gas separators and reactor internals. The halogen containing compounds and their products necessary for platinum redispersion are highly toxic as well.
Current regeneration methods of a reforming catalyst take several days, and the equipment is exposed to hydrochloric acid during this period. In conventional processes, the oxygen which remains in the catalyst bed after regeneration is purged from the catalyst at low pressure, typically less than 50 psig, and at temperatures around 400° F. The hydrogen which is then introduced to reduce the catalyst is brought in at this low temperature. The required additional cooling to bring the catalyst to around 400° F., and the additional heating to return the catalyst to reaction temperature adds many hours for the regeneration. Thus, there is a need for catalytic reforming processes wherein the catalyst regeneration process is conducted at effectively moderate reaction temperatures and pressures, using gas compressors, pumps and valves which are employed during the reforming process, which results in substantial operating economies as compared with processes and systems of the prior art.